A fuel cell system is a power-generating device that generates electrical energy through electrochemical reaction of hydrogen-containing fuel with air. Since it has the advantages of low pollution, low noise, and high efficiency, the fuel cell system is an energy technique meeting nowadays requirements. Among various fuel cell systems, the proton exchange membrane fuel cell (PEMFC) and the direct methanol fuel cell (DMFC) are the two most common fuel cell systems.
Please refer to FIG. 1 that shows a conventional flow field plate module 1 for a fuel cell system. As shown, the flow field plate module 1 includes a membrane electrode assembly (MEA) 11, and an anode flow field plate 12 and a cathode flow field plate 13 separately located at two opposite outer sides of the MEA 11. The MEA 11 consists of a proton exchange membrane (PEM), an anode catalyst layer 112, a cathode catalyst layer 113, an anode gas diffusion layer (GDL) 114, and a cathode gas diffusion layer 115. The anode flow field plate 12 and the cathode flow field plate 13 are normally made of graphite, and are provided on respective inner side surface with flow channels 121, 131, through which reactants flow.
To pump methanol-water solution through the flow channels 121 on the anode flow field plate 12 to react with the anode catalyst layer 112 in the MEA 11, good flow channel design is needed to enable uniform reaction of the methanol-water solution with the anode catalyst layer 112. In addition, since anode product, such as carbon dioxide, is produced in the reaction of the methanol-water solution with the anode catalyst, the flow channel of the anode flow field plate designed must also be capable of successfully discharging the anode product.
The conventional flow channels on the anode flow field plate may be differently designed. FIG. 2 shows a serpentine flow channel design, and FIG. 3 shows a parallel channel design. In the serpentine flow channel design, a continuously winding path, i.e. a serpentine flow channel 121a, is provided on the anode flow field plate 12. The serpentine flow channel 121a is communicably connected at an end to an anode fuel inlet 14, and at the other end to an anode fuel outlet 15. In the parallel flow channel design, a plurality of parallelly connected paths, or flow channels 121b, are provided on the anode flow field plate 12. One common end of the plurality of parallel flow channels 121b is communicably connected to an anode fuel inlet 14, and another common end of the plurality of parallel flow channels 121b is communicably connected to an anode fuel outlet 15.
Both the serpentine and the parallel flow channel design achieve the purpose of transporting fluid, that is, the methanol-water solution. However, these two types of flow channel design have respective disadvantages. For example, the serpentine flow channel 121a is relatively long to cause excessively large pressure loss in the course of transporting the fluid in the direction as indicated by the arrows in FIG. 2. Therefore, a pump providing a relative high pressure is needed to drive the methanol-water solution to flow through the serpentine flow channel 121a. Moreover, the methanol-water solution at the upstream of the serpentine flow channel 121a reacts at the anode catalyst before it flows to the downstream. The methanol-water solution at the downstream of the serpentine flow channel 121a therefore has a concentration lower than that of the solution at the upstream. That is, the serpentine flow channel 121a has the problem of changing methanol concentration diminishingly from the upstream to the downstream.
On the other hand, while the parallel flow channel design overcomes the problem of changing methanol concentration between the upstream and the downstream serpentine flow channel, another problem with non-uniformly distributed flow in the parallelly arranged flow channels 121b is found. When the produced carbon dioxide accumulates in the flow channels, increased flow resistance is produced in the flow channels. Since the fuel tends to flow toward flow channels 121b that have somewhat lower flow resistance, it is difficult to discharge the produced carbon dioxide.